The present invention relates to a multistage liquid-solid fractional extraction apparatus and more specifically, to a multistage liquid-solid fractional extraction apparatus used for separation of substance by making use of a difference in the adsorption power of the substance existing in solution to solid.
As a method to remove or to recover a substance in solution by means of its adsorption to solid, a decoloration by the active carbon, a removal of the ion by the ion-exchange polymer or the like are widely known. These procedures mostly finish in one step, however in case of separating each kind of substances by making use of the difference in each adsorption power to a specific solid, the chromatography is widely used. The chromatography is a technology in which a fine solid in a uniform shape is packed in the column, liquid or gas as a mobile phase is flowed therein, and a lot of substances existing in a solution or gas are separated by making use of a distribution difference of substances in between solid and liquid or between solid and gas, and is an extremely effective device which can carry out a mutual separation by making use of a small difference of the distribution coefficients in case of the separation of a small amount of mixture.
As described above, the chromatography is an effective separation device for separation of a small amount of mixture, but it cannot be said that it is an appropriate device for separation of a large amount of mixture. Namely, although a lot of trials have conventionally been done to separate a large amount of mixture by employing a chromatographic technique and by enlarging the column size, it has not been come yet.
In order to firmly carry out the separation of a substance by chromatography, it is necessary to uniformly flow a mobile phase in a solid phase packed in the column, and this is also the case when the column size is enlarged to treat a large amount of sample. However, in the case that the column size becomes larger and the cross section becomes wider, it becomes more difficult to make a resistance against fluid uniform in a wide cross section as a whole, giving a difference in a fluid resistance in the column, so that the flow rate becomes rapid at a place where the fluid resistance is small and the flow amount of the mobile phase becomes large at a part of the column cross section, i.e. a so-called channeling occurs. In such a case, the uniform flow of the mobile phase, which is a fundamental condition of the chromatography, is not achieved, and as a result of course, the separation efficiency deteriorates significantly.
Additionally, in case that a substance exists, which has a big adsorption power for solid and which scarcely elutes once it adsorbs, and that such substance is adsorbed by solid, passages become narrower by that extent and the resistance of the mobile phase against the flow increases, resulting to a change of the resistance against the mobile phase in each cross section of the column whenever a mixed sample is flowed. Therefore, even if the solid is initially packed uniformly, the flow resistance varies whenever a sample is flowed, and furthermore, the chromatographic procedure cannot directly be applied to the separation of a large amount of sample, since it is impossible to control the variation. Further, the fact that such a phenomenon does not occur in a usual chromatography is owing to the presence of only an extremely small amount of the irreversibly adsorptive substance, even if any, showing that a considerable number of treatments are possible until it affects the flow resistance of the column. In fact, in case of the analysis in the chromatography, it is widely known that a performance of the column degrades as the number of times of a sample injection increases.
Thus, although the chromatography is extremely effective as a separation device of a small amount of mixture, it is not possible to get a reproducible result in separation of a large amount of mixture, and there has been a big demand to develop a device by which a large amount of mixture can be separated in a similar procedure as a chromatography.
In such circumstances, this applicant previously provided a multistage liquid-solid fractional extraction apparatus by which a separation procedure for a large amount of mixture could firmly and effectively be carried out by making use of the distribution difference in the liquid chromatography. However, when a stirring apparatus such as a magnetic stirrer or screw as a stirring device, by which a liquid-solid mixture is directly stirred in a mechanical way, is employed, the solid (adsorbent) is ground by the friction with the stirrer or the like in a long lasting stirring procedure to a fine powder state, and possibly, a stable and constant state cannot be kept due to the flowing out from an efflux protecting device, for example, a filter or the like, which is equipped with at a liquid outlet part, or to the occurrence of the clogging. Further, in cases of employing a large volume of container or of a high solid concentration, the driving force becomes excessive, and the uniform stirring cannot be expected, whereby a deterioration of the stirring efficiency is anticipated.